Animal feeds are supplemented with individual amino acids according to the needs of the animals. The supplements used in addition to chemically produced methionine include the fermentatively produced amino acids lysine, threonine and tryptophane. Thus in pigs, for example, the ratio of these three amino acids found to provide optimum feed utilization, i.e., minimum liquid manure production, is lysine:threonine:tryptophane=100%: 65%: 18%, taking lysine as 100% (see T. C. Wang, M. Fuller, British Journal of Nutrition, 62, 77-89 (1989).
Supplementing animal feeds e.g. with L-lysine has hitherto been carried out predominantly with L-lysine monohydrochloride having an L-lysine content of 80%. Since L-lysine is produced by fermentation, it is necessary to remove all other components of the crude fermentation broth by elaborate process steps before the L-lysine is converted into the monohydrochloride and the latter must then be crystallized.
Therefore, there has been no lack of attempts in the past to avoid the expensive process of preparing feed amino acids, in particular pure L-lysine monohydrochloride, and to convert the crude fermentation broth by a less expensive process into a solid animal feed. None of these experiments, however, has provided an economically acceptable result. Simple dewatering of the crude fermentation broth resulted in a highly hygroscopic, sticky concentrate which could not be used as an animal feed. For obtaining a pourable and storage stable product, it was necessary to incorporate a large quantity of a wide variety of additives in the concentrate, but this reduced the concentration of amino acid, which in many cases was already low.
Published European Patent application EP-B 122 163 discloses a process by which a crude fermentation broth, which can be dried to a solid and stable product, can be obtained if special fermentation conditions are observed. This product is obtained by dewatering the whole fermentation broth, but the L-lysine content of the product is only 35 to 48 percent by weight, which is considerably lower than that of L-lysine monohydrochloride. The biomass left in the product in this case acts as an additive which improves the free-flowing character of the product.